Throughout this specification, the term "optical" is intended to refer to that part of the electromagnetic spectrum which is generally known as the visible region, together with those parts of the infra red and ultra violet regions which are capable of being transmitted by dielectric waveguides such as optical fibres.
An optical fibre telecommunications network is used to distribute information (optical signals) from one or more transmitting stations to one or more receiving stations. For telecommunications purposes, a passive optical network (PON), such as TPON (telecommunications over a passive optical network), is advantageous in that it permits telecommunications over a network using a single transmitter (a laser located at exchange connected to the network). The main advantage of TPON is that it enables the sharing of optical network fibres, and the opto-electronic equipment that serves them. TPON involves the use of optical splitter to pass optical signals from the exchange laser to receivers (typically telephones) at the customers' premises. A preferred split level is a 32-way split, accomplished by a four-way split at the cabinet level, and by eight-way splits at the four distribution points (DPs) fed by the cabinet.
In a preferred form of TPON, known as street TPON, the final drop to the customers is by copper pairs, and the fibre terminates at the DPs. In this case, each DP is provided with opto-electronic conversion/switching equipment, and this equipment needs to be powered electrically.
One way of powering such equipment would be to provide a mains electricity feed. The disadvantage of this is the expense involved in providing the transformer and control equipment necessary to power the opto-electronic conversion/switching equipment. Moreover, as DPs are commonly sited at the tops of poles, this transformer and control equipment would have to be sited in footway boxes, and this leads to high installation costs. Similarly, the provision of batteries to power the opto-electronic conversion/switching equipment would lead to high installation costs, as these too would need to be sited in the ground.